50g is NOT to small for ONE 8" piranha. My brother raised 6 baby piranhas in a 10 gallon aquarium, and then moved them into a 35 gallon tall when they were all 8 inches long and they were all perfectly healthy. None of them were skittish or anything like that. The rule of thumb is that one inch of fish needs one gallon, so an eight inch fish only needs 8 GALLONS, not 150.
You couldn't be more wrong.
The height of the tank doesn't matter anyways, that's just wasted space for piranhas and I find it hard to believe that rbp's weren't skittish. They're one of the biggest sissy fish alive and they might have been alive but certainly weren't healthy.
50g
IS too small for 1 8" rbp. (Not to mention the BS lies you stated about having 6 rbp's that were 8" in a 10g tank, which is a lie and you know it. If you don't know something is one thing but don't lie to save yourself and try not looking stupid or to try and show someone else up that took their time to try and help you AND your fish's best interest, because that BS you just spewed forth may be believed by someone out there reading that crap and they may think it's ok and try it. The fish will suffer as will the aquarist that tries it, both monetarily and emotionally if attached to the fish. I love piranhas and don't like that at all.)
The "rule of thumb" you cite is incorrect and terribly dangerous information and doesn't take into account the MASS or BIOLOAD of fish like a cichlid or piranha. Maybe if you're talking about guppies then 1" per gallon could be used as a general rule of thumb.
You can't even get enough filtration on a 35g for an rbp that is messy without it swimming against too much current constantly. RBP's and most Pygo's don't come from heavy current waters like Serrasalmus do.
There is NO WAY an 8" piranha can live in an 8g tank.
You don't know the most rudimentary of things in piranha keeping like if an 8" P. nattereri will kill 2" ones when added later to his territory. (Which is more than ok and why you asked the question here) but you know if piranhas are happy in too small of aquaria and what they need to thrive.
I have living proof in my room. My brother gave me one of his piranhas and i'm keeping it in a 20 gallon and it is perfectly healthy. I'm just sick of people always suggesting ridiculusly sized aquariums for just one fish.
I'm not suggesting rediculously sized aquaria. I'm suggesting a minimum of 75g for 1-3 rbp's.
